1. Field of the Invention
Embodiments of the present invention relate to X-ray medical imaging, and in particular breast radiography or mammography. Embodiments of the present invention notably relate to X-ray mammography devices comprising image processing units.
2. Description of the Prior Art
Conventional X-ray imaging systems allow the acquiring of projection images of an object of a subject, typically a female patient's breast, via the passing of X-rays through the object.
However, when X-rays pass through the object, a phenomenon of scattering is observed, resulting from interaction between the X-rays and the different constituent materials of the object.
This scattering of X-rays has an impact on the image obtained which then exhibits degradations.
Several approaches have been put forward to reduce or compensate this scattering of X-rays, either using physical elements or using pre or post-acquisition processing methods.
The approaches using physical elements make use of anti-scatter mechanical grids arranged between the object and the X-ray sensor, the mechanical grids being formed to absorb all or part of scattered X-ray radiation. The document “Mammography grid performance”, Radiology 210, 227-232 (1999) by P. S. Rezentes, A. de Almeida and G. T. Barnes presents an example of anti-scatter mechanical grids. However, these mechanical grids absorb part of the emitted X-rays, and it is therefore necessary to increase the emitted X-ray dose to maintain a good quality image. In addition, these anti-scatter grids do not fully prevent scattered radiation; the transmission of scattered radiation through said anti-scatter grids under standard mammography conditions being of the order of 15 to 20%.
A method for estimating and correcting this residual scattered radiation has already been proposed and is described in document U.S. Pat. No. 4,677,681. This method is based on the use of masks opaque to X-ray radiation inserted in the beam between the source and the examined object, so as to estimate the quantity of X-ray radiation scattered by the object.
This method nonetheless requires the acquisition of at least one additional image compared with conventional imaging, this image being solely intended to determine the contribution of scattered radiation to the image insofar as the images taken in the presence of opaque elements cannot be used for diagnosis. This aspect could be acceptable for the acquisition of sequences of several images, but this is not so for ordinary radiography e.g. mammography in which it is sought to record a single image.